Generally, in the manufacture of large-scale Li-ion power battery cells, the pole-piece pockets are manufactured before the pole-pieces are stacked. A method for such manufacture comprises wrapping a pre-clipped pole-piece with two films, vertically thermal-welding a single joint once in the manner of thermal welding, conducting a transversely thermal-welding to encapsulate the pole-piece of which the tab is exposed out. The deficiencies of such method are that the distance between two adjacent vertical welding joints and the quality of the pole-piece pockets cannot be ensured, and the risk of malfunction is high.